Systems and methods for controlling power in an electrosurgical generator

Abstract

The electrosurgical systems and corresponding methods of the present disclosure involve an electrosurgical generator, sensing circuitry, and a controller. The electrosurgical generator includes a radio frequency (RF) output stage that supplies power to tissue. The sensing circuitry measures impedance of tissue. The controller controls the power supplied from the RF output stage to track a nonlinear power curve until the power supplied from the RF output stage has reached a predetermined peak power of the nonlinear power curve. The controller further determines whether a tissue reaction has occurred based on impedance measured by the sensing circuitry and controls the power supplied from the RF output stage during a cooling phase if the controller determines that a tissue reaction has occurred. The controller may further control the power supplied from the RF output stage to track a linear power curve.

What is claimed is: 
     
       1. An electrosurgical generator, comprising:
 a radio frequency (RF) output stage configured to supply power to tissue; 
 sensing circuitry configured to measure an impedance of the tissue; and 
 a controller configured to:
 control the power supplied from the RF output stage to track a predetermined nonlinear power curve, the predetermined nonlinear power curve corresponding to a third-order polynomial and having a first portion, a second portion after the first portion, and a third portion after the second portion, wherein the second portion includes second rates of increase of power, and rates of increase of power of the first portion and the third portion are less than the second rates of increase of power; 
 determine whether the measured impendence of the tissue exceeds an impedance threshold; 
 control the power supplied from the RF output stage to terminate tracking of the predetermined nonlinear power curve and to enter a cooling phase when the controller determines that the measured impendence of the tissue exceeds the impedance threshold while tracking the predetermined nonlinear power curve; 
 control the power supplied from the RF output stage to track a predetermined linear power curve when the controller determines that the measured impendence of the tissue does not exceed the impedance threshold and the power supplied from the RF output stage has reached a predetermined peak power of the predetermined nonlinear power curve; 
 determine whether a tissue reaction has occurred based on the impedance measured by the sensing circuitry while tracking the predetermined linear power curve; and 
 control the power supplied from the RF output stage during the cooling phase. 
 
 
     
     
       2. The electrosurgical generator according to  claim 1 , wherein the controller includes a memory storing a look-up table including a plurality of predetermined nonlinear power curves, a plurality of predetermined linear power curves, and a plurality of sizes of electrodes of electrosurgical instruments usable with the electrosurgical generator, and
 wherein the controller is configured to receive an electrode size and select the predetermined nonlinear power curve from the plurality of predetermined nonlinear power curves and the predetermined linear power curve from the plurality of predetermined linear power curves based on the received electrode size. 
 
     
     
       3. The electrosurgical generator according to  claim 1 , wherein the controller is further configured to adjust a parameter of the predetermined linear power curve based on a surface area of an electrode of an electrosurgical instrument usable with the electrosurgical generator, and
 wherein the parameter of the predetermined linear power curve is selected from the group consisting of a slope and a duration. 
 
     
     
       4. The electrosurgical generator according to  claim 3 , wherein the larger a surface area of the electrode is, the shorter a duration of the predetermined linear power curve is and the larger a slope of the predetermined linear power curve is, and
 wherein the smaller the surface area of the electrode is, the longer a duration of the predetermined linear power curve is and the smaller a slope of the predetermined linear power curve is. 
 
     
     
       5. The electrosurgical generator according to  claim 1 , wherein the controller is further configured to adjust a parameter of the predetermined nonlinear power curve based on a surface area of an electrode of an electrosurgical instrument usable with the electrosurgical generator. 
     
     
       6. The electrosurgical generator according to  claim 5 , wherein the parameter of the predetermined nonlinear power curve is selected from the group consisting of starting power, a duration, a shape, slopes, the predetermined peak power, and combinations thereof. 
     
     
       7. The electrosurgical generator according to  claim 5 , wherein the larger a surface area of the electrode is, the longer a duration of the predetermined nonlinear power curve is and the smaller the predetermined peak power of the predetermined nonlinear power curve is, and
 wherein the smaller the surface area of the electrode is, the shorter a duration of the predetermined nonlinear power curve is and the larger the predetermined peak power of the predetermined nonlinear power curve is. 
 
     
     
       8. The electrosurgical generator according to  claim 5 , wherein the electrosurgical instrument includes a Radio Frequency Identification tag storing the parameter of the predetermined nonlinear power curve. 
     
     
       9. The electrosurgical generator according to  claim 1 , wherein the controller includes a memory storing a look-up table including a plurality of predetermined nonlinear power curves and a plurality of sizes of electrodes of an electrosurgical instrument usable with the electrosurgical generator, and
 wherein the controller is configured to receive an electrode size and select the predetermined nonlinear power curve from the plurality of predetermined nonlinear power curves based on the received electrode size. 
 
     
     
       10. The electrosurgical generator according to  claim 1 , wherein the controller is further configured to:
 determine a minimum impedance based on the measured impedance; and 
 determine whether the tissue reaction has occurred based on the minimum impedance and a predetermined rise in the impedance of the tissue being treated. 
 
     
     
       11. The electrosurgical generator according to  claim 1 , wherein the controller is further configured to:
 determine whether the tissue reaction has occurred within a first predetermined period; and 
 stop the power supplied from the RF output stage and issue a re-grasp message, if the controller determines that the tissue reaction has occurred within the first predetermined period. 
 
     
     
       12. The electrosurgical generator according to  claim 1 , wherein the controller is further configured to determine whether the tissue reaction has occurred within a second predetermined period, and control the power supplied from the RF output stage to restart tracking of the predetermined nonlinear power curve if the controller determines that the tissue reaction has not occurred within the second predetermined period. 
     
     
       13. An electrosurgical system, comprising:
 an electrosurgical generator including:
 a radio frequency (RF) output stage configured to supply power to tissue; 
 sensing circuitry configured to measure an impedance of the tissue; and 
 a controller configured to:
 control the power supplied from the RF output stage to track a predetermined nonlinear power curve, the predetermined nonlinear power curve corresponding to a third-order polynomial having a first portion, a second portion after the first portion, and a third portion after the second portion, wherein the second portion includes second rates of increase of power, and rates of increase of power of the first portion and the third portion are less than the second rates of increase of power; 
 determine whether the measured impendence of the tissue exceeds an impedance threshold; 
 control the power supplied from the RF output stage to terminate tracking of the predetermined nonlinear power curve to enter a cooling phase when the controller determines that the measured impendence of the tissue exceeds the impedance threshold while tracking the predetermined nonlinear power curve; 
 control the power supplied from the RF output stage to track a predetermined linear power curve if the controller determines the measured impendence of the tissue does not exceed the impedance threshold and the power supplied from the RF output stage has reached a predetermined peak power of the predetermined nonlinear power curve; 
 determine whether a tissue reaction has occurred based on the impedance measured by the sensing circuitry while tracking the predetermined linear power curve; and 
 control the power supplied from the RF output stage according to the cooling phase; and 
 
 
 an electrosurgical instrument coupled to the electrosurgical generator, the electrosurgical instrument including at least one electrode.